I think it is fine... as long as they dont make you miss "that shot", are courteous, and know what is and isnt allowed, they are only doing their job in enquiring (just think of the stick they get if it turns out the one they didnt go up to question was actually a terrorist and on a reccy mission).  Once they overstep that mark and violate your right to take a photo then i would object. But generally (probably because i havent experienced it yet) i think it is a good thing they are actually being alert to the possibility.

Remember if you are stopped to ask to take their photo - get your candid street portraiture mindset going and a great addition to your portfolio! :biggrin:

"In every colour, there's the light.
In every stone sleeps a crystal.
Remember the Shaman, when he used to say:
Man is the dream of the Dolphin"

Rich Meadows Photography